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BTU and EER – Air Conditioner Basics Explained

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A surefire way to make it through hot summers is by turning on the AC. Don’t have one yet? Well, then it is time that you start looking into air conditioner selections to pick the one that has everything you are looking for. Are you confused by the terminology? Do not fret as we will explain in the following more about the two terms you always bump into when you look for AC units – BTU and EER. Their roles are more important than you could imagine when it comes to highlighting the performance and efficiency of the system, so stick with us till the end to get your facts straight about these two essential stats.

What Does BTU Mean?

BTU definition: It is short for British Thermal Units (despite the name, this rating is used at a worldwide scale, not being unique to the U.K.), and it is a measurement of energy. One BTU serves the purpose of indicating how much energy is required to raise the temperature of one pound of water by 1°F at sea level.

Since the rating indicates energy in correlation with heat, its presence on the labels of heaters is easily understandable. But what does it have to do with cooling systems? Why are BTUs used to rate their performance as well? To understand this, you first need to know how exactly an AC unit works. What they actually do is remove the heat from the room rather than adding cool air. This is where BTUs factor in as they show how much energy is needed for the AC to remove the heat using the compressor system.

Why Does BTU Matter?

To get the right AC unit you have to size it properly. For this, you must select the proper amount of BTUs needed for the area in which you will use the cooling system. Higher ratings imply that more power is provided, and are attributed to units that cover larger areas. Beware of this last part as it is important – if you have a small-size space, don’t opt for an AC with an absurdly high BTU rating in the idea that it will cool off the room quicker because this is a mistake that will end up costing you (literally!).

If the AC is too powerful, it might cool the room quickly, but this is not the sole purpose of the unit. In its operation, it is supposed to remove moisture from the air as well, something it won’t have time to do if it turns off after too little time. There is the issue of it cycling on and off more often than it should so that it can preserve your preferred temperature. This, in turn, implies that the unit will wear out and break down sooner than it should.

Be cautious and size the AC right! Check out our best dual hose portable air conditioners to be provided with a wide range of models when it comes to space coverage and cooling power, finding what you need here easily.

What BTU Rating Do You Need?

So, how do you figure out exactly what BTU power you need? Well, it is a simple formula to use and determine a preliminary value for the air conditioner. Just measure the room’s square footage, and multiply it by 20. Now, you have a preliminary result in regards to proper BTU rating.

Additional considerations: If you need the AC for the kitchen, add 4,000 BTUs to the result of the calculation. If the room gets a lot of sun exposure, increase the result by 10%. Do the opposite if the room is mostly shaded (decrease by 10%). The number of people influences the result too. If more than two folks are in the room at the same time, you must add another 600 BTUs for each person.

After you finish the preliminary calculation and tweak it according to these considerations, you finally get the answer to your question – that is the amount of BTUs you need for the AC to provide. This is how you size the cooling system, so beware that BTUs are the fundamental factor in proper sizing and AC efficiency in cooling specific spaces.

What Does EER Stand For?

EER definition: It is short for energy efficiency ratio. This rating is utilized to indicate the amount of BTUs per hour transferred for each watt-hour of electrical energy the AC uses.

There is a formula that you can use to calculate the EER rating of an AC, and it goes as follows: cooling output (expressed in BTUs per hour) divided by energy input (expressed in watt-hours). So, if the AC uses 1,400 watts to provide 14,000 BTUs, then the EER rating you will spot on the spec sheet is 10.

What Is a Good EER Rating for an Air Conditioner?

In the long-run, this is the stat that likely interests you the most as it shows how energy-efficient the system is. All AC units built after 1990 have a minimum EER rating of 8, which is decent. If you live in an area with a mild climate, you can go for an EER 9 rated AC without it drawing too much power, whereas, if you live in a hot climate area, you should opt for units rated EER 10 and above.

Tip: We would advise that you go for EER 10 or higher regardless of the climate in your area. Energy costs tend to be high, and the AC is a system that is intensely used when summer comes, so the higher the EER the better as you will not spend too much money when the bills come.

Other Aspects You Must Look Into when Buying an AC Unit

Now that we technically covered explaining sizing and energy efficiency by defining BTU and EER and discussing their importance, it is time to move on. Let’s see what other aspects of interest matter when buying an AC to help you make a smart pick:

1. How much does it dehumidify?

Through its operation, the AC also reduces air moistness levels as it extracts humidity from the hot air removed. If you live in a hot, damp climate area, it is especially important to look into the dehumidification capacity of the AC before you buy as it could save you from having to separately acquire a room dehumidifier. If your dehumidification needs are high, the bigger the capacity of the AC is, the better.

The AC might wick away moisture, but it does this for the room you place it in exclusively. If your high humidity issues step from an excessively damp crawlway, see here our selections of the best crawl space dehumidifiers to stabilize and upkeep proper moisture levels in this more pretentious area of the property.

2. Does it come with a programmable thermostat?

Control over the air conditioner is what you must aim for to create ideal thermal comfort indoors. This is achievable only if the unit features a programmable thermostat as it allows you to set the temperature you want the system to work and maintain. It works similarly to the humidistat that you find in humidifiers and dehumidifiers and that controls their operation to upkeep your preferred humidity level.

3. Is the filter good enough?

Indoor air quality is poor without the use of air filtration media. While nothing beats the efficiency of having an air purifier that specifically tackles the issues you are faced with, whether it is the presence of foul odors, tobacco smoke, or even dust, a little extra help from the AC does not hurt either. Not to mention that the reason why the filter is there in the first place is to keep the particles in the air from damaging the system.

Read our guide on how to clean a window air conditioner to learn more about filter upkeep – when and how to do it.

4. Can it heat the room too?

To make the AC a year-round appliance, look into a model that you can program to warm up the place when winter comes too. It is pointless to dig in further into the topic as it is self-explaining why this is a good feature for the system to have, eliminating the need for you to separately acquire and install a heating system.

5. Does it feature a timer?

We cannot stress enough about the usefulness of a timer on the AC. Think of it like this – the feature lets you program exactly when the AC should start cooling the room and how long it should stay on. This means that when it’s the middle of August and you come home from a tiring day of work, having to sit through traffic in intense heat, you open the door to find the place already at a perfect temperature to cool off. There is no point in continuing from here, you likely understand now why it is a must-have feature.

Tips to Make the Most Out of Your Air Conditioner

  1. When you want to amp its cooling efficiency without forcing the system too much, put a tray of cool water in front of the unit’s vent. As the cool air flows over the tray, it produces a cool mist breeze that keeps you way more comfortable than simple cold air would.
  2. Look into the best misting fans if you like the idea of cooling off with a breeze of moisture that hits your body when you are feeling hot.

  3. Close all windows in the room so that hot air does not come in, and the cool air does not go out either. This goes for the doors as well.
  4. Don’t take your showers too hot because the hot steam might get into the room where the AC is and tamper with its efficiency.
  5. Aside from the room dehumidifier, turn off all appliances that have no purpose at that moment and that generate heat.
  6. Insulate your home! Insulate the attic, the basement, encapsulate the basement, and make sure that the house itself is up to the highest standards. This doesn’t only help with AC cooling efficiency but it reduces costs on utility and electric bills as a whole as it optimizes the work of other household appliances as well, making them work more efficiently.
  7. Change the air filter on time, as instructed in the accompanying user manual. Failure to do so negatively impacts the performance of the AC and it reduces its ability to clean the air in its operation as well.
  8. Once per year, make it a point to call in a professional and check the AC top to bottom, searching for potential clogs, leaks, issues that need repairing, and so on. This way, you make sure that the AC is properly maintained and serviced, and that it will last for a long time.
  9. A ceiling fan can help out more than you can imagine. It draws an insignificant amount of power when it runs, and it will help circulate the cool air better in the room. Thus, you won’t have to set the AC thermostat as low as you normally would have to achieve thermal comfort.
  10. During the colder hours of the day, keep the windows open to naturally reduce the temperature indoors. This won’t hurt when it comes to air purity either as you let the stale air out of the room too.
  11. Try to cook early in the morning or late at night if possible. Maybe even have barbecues outside more often if you have a backyard and a grill. The idea is to do anything you can to keep the heat out.

Final Thoughts

BTU is the main factor you need to guide yourself by when you look for an AC as it indicates whether the system is the right capacity for your needs or not, whereas EER indicates how energy-efficient it is, a factor that matters because you would not want to spend a fortune on the bills. Now that you know what they stand for and their importance, as well as what other elements matter when buying an AC, you are ready to go and pick the cooling system that will create perfect indoor conditions for you even during the hottest day of the year.

Tobey Hunter
Tobey Hunter
Tobey is the editor-in-chief at Optima Institute, his prior experience as a niche product reviewer in air quality improvement systems helping shape his path to conduct thorough research toward selecting and analyzing products so that customers are satisfied with the provided recommendations. During his carrier, Tobey also gathered technical input that makes him well versed in understanding advancements in modern systems, helping readers in turn to better understand how modern devices help improve life quality.